1. Field of the Invention
The present invention relates generally to linear electric motors, and more particularly, to stators, called platens, for linear motors operating in the plane.
2. Description of Prior Art
Linear motors operating in the plane, sometimes referred to as planar linear motors and hereafter referred to as planar motors, are able to rapidly and precisely move within a plane of motion, as opposed to simpler linear motors which are capable of moving only in a straight line. Planar motors operate on a planar stator element referred to as a platen. A feature is that multiple planar motors can operate together on a single platen. Planar motors can trace straight line paths in any direction on the platen, or can move in curved paths, e.g., in a circle. As is well known, these attributes can make the planar motor an essential part of very versatile motion systems. Such systems have many applications, especially in manufacturing. Several companies currently market manufacturing systems based on planar motors.
A popular type of planar motor (U.S. Pat. No. 3,376,578 to Sawyer) provides linear motion in two orthogonal directions in the plane as well as small rotations in the plane. Such a planar motor generally combines four linear-motor sections into a single housing and is capable of producing forces and torques in the plane. The planar motor is magnetically attracted to a patterned iron platen surface while being forced away from the surface by an air bearing film; the equilibrium separation being typically 10 to 15 xcexcm. The motor sections have fine teeth (typically 0.02 in. wide on a 0.04 in. pitch) and the platen has a two-dimensional array of square teeth of corresponding width and pitch. After chemical or physical machining, the platen surface is planarized using epoxy to form the air-bearing operational surface. The planar motor rides above the platen surface in operative juxtaposition, or, if the platen is inverted, hangs below the platen surface in operative juxtaposition.
Another type of planar motor (U.S. Pat. No. 6,175,169 to Hollis et al.) is of a closed-loop type incorporating an AC-magnetic position sensor, offering advantages of higher speeds and accelerations, greater precision, and the ability to reject mechanical disturbances.
Yet another type of planar motor (U.S. Pat. Nos. 5,777,402, 6,005,309, and 6,104,269 to Chitayat) has a housing containing energized coils. This type of planar motor operates over a platen containing a plurality of permanent magnets embedded in its operational surface. As in the previous type of planar motor, an air bearing separates the planar motor from its platen surface. The roles of platen and motor can be reversed, i.e., the platen can contain an array of coils and the motor can contain only permanent magnets. This arrangement trades the complexity of electrically sequencing a large number of platen coils for the simplicity of a motor needing no electrical connections.
For the aforementioned types of planar motors, platens are made in various sizes to fit intended applications. For example, a popular size platen is 37 inxc3x9752 in., but smaller and larger sizes exist. A great difficulty is that the correct size must be chosen carefully before the application is carried out. Generally, the platens are expensive items. If a platen size turns out to be too small, e.g., restricting the motion of multiple planar motors operating over its surface, it must be discarded in favor of a larger one. On the other hand, if a platen is made much larger than necessary, money is wasted.
Larger platens are sometimes fabricated by permanently joining together smaller platens during the manufacturing process. Misalignment of critical operational features such as the aforementioned fine teeth often occurs at the interface crack between these smaller platens. For linear motors, U.S. Pat. No. 5,887,334 to Dooris, et al. teaches a method of splicing together sections of linear motor platens to produce longer platens. Unfortunately, this method cannot apply to planar motor platens.
What is needed is way to make platens for planar motors in tile form to enable their joining and unjoining in the field by the end user of such planar motors to produce platen ensembles of various sizes and topologies to fit the application. The prior art fails to address this need.
Accordingly, several objects and advantages of the present invention are:
Precision platen tiles for planar motors with features including:
(a) rectangular platen tiles of substantial rigidity with operational surfaces of substantial planarity comprising stators for multiple planar motors operating thereon;
(b) rectangular platen tiles whose operational features, e.g., ferromagnetic teeth, permanent magnets, or electrical coils, are precisely aligned with respect to the edges of the rectangular tiles;
(c) rectangular platen tiles of operational feature periodicity xcex with edges located precisely xcex/2 from these features, permitting unbroken continuity of features when two or more platen tiles are joined together;
(d) rectangular platen tiles incorporating a surrounding structural frame therein of substantial strength permitting large clamping loads to be applied without appreciable deflection of the platen tiles"" operational surfaces;
(e) precision height adjustment mechanisms for precisely setting the height and levelness of platen tiles;
(f) clamping mechanisms incorporating a first precision reference surface ensuring that the operational surface of two mating platen tile surfaces are accurately aligned regardless of the thickness of the two platens, and a second precision reference surface ensuring that the edges of two mating platen tiles are accurately aligned;
(g) clamping mechanisms incorporating a first precision reference surface ensuring that the operational surface of three mating platen tile surfaces are accurately aligned at a common corner regardless of the thickness of the three platens, and second and third precision reference surfaces ensuring that the edges of three mating platen tiles are accurately aligned; and
(h) magnetic or non-magnetic polymer filler to bridge unavoidable small gaps in the interface crack between adjacent platen tiles.
The features (a-h) taken together, permit large areas of platen to be swiftly assembled in the field by semi-skilled workers using a few simple tools. Further, the ensemble of light weight platen tiles can be deployed with various topologies which include L- and T-shaped configurations, according to the needs of the application. A collection of planar motors can travel over the operational surfaces of the ensemble, freely crossing the interface crack between tiles. The configuration of tiles can be easily modified in the field as conditions warrant. When the application is completed, the ensemble can be swiftly dissassembled into its component parts and re-used for a different application. Thus the invention of field-joinable platen tiles permit the designer of a small, medium, or large motion system based on planar motors a degree of flexibility hitherto unobtainable. There is a tremendous need for such flexible motion systems in a broad sector of manufacturing industries.
Further objects and advantages of the invention will become apparent from a consideration of the drawings and ensuing description.
A precision field-joinable platen tile which may be combined with other like tiles to provide an unbroken, continuous operational platen surface or stator upon which multiple planar motors can freely operate.
A set of provisions for supporting, leveling, aligning, and joining the above described platen tiles.